Proximity fuse



Sept. 5, 1961 J. B. CRAFT 2,998,775

PROXIMITY FUSE Filed Feb. 9. 1956 INVENTOR. JOHN B. CRAFT a TTOR/VEW 2,998,775 PROXIMITY FUSE John B. Craft, 11812 Lakewood Blvd, Downey, Calif. (709 W. Atlantic St., Philadelphia 40, Pa.)

Filed Feb. 9, 1956, Ser. No. 564,588 v p 4 Claims. (Cl. 102-702) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposeswithout the-payment of any royalties thereon or therefor.

This invention relates to missiles and fuses, and more particularly to a missile fuse of a proximity type operable by sensing an ionized trail of a jet target in a tail chase aspect.

Proximity type fuses have for the most part replaced impact type detonators as the'primary control over missile detonation. Some proximity fuses are designed to be actuated by air pressure impulses imparted by a target in flight, and others are controlled by electromagnetic radiations transmitted and received by the missile. Still another type of proximity fuse operated electrically is represented by US. Patent No. 2,505,042 disclosing an anti-aircraft projectile which relies on the leakage of electrostatic charge accumulated on target surfaces to ignite the fuse when the diiference in potential between the target and the projectile is sufiicient to supply a required spark. This type of fuse has disadvantages in that it is limited in use, relies on a tracer. bearing projectile, and requires a relatively high electrical potential. The electromagnetic fuse is predominant in the field although it is complex, costly, and has a low reliability.

According to the present invention the missile fuse is provided with a means for sensing the proximity of a jet target in flight by the presence of its ionized air trail and for detonating the primer when the missile is at lethal range. The fuse is particularly suitable for use in unguided or guided air-to-air missiles fired at a jet aircraft in a tail chase aspect. In the preferred embodiment the ion sensing means comprises a capacitor having spaced electrodes so arranged that the air sampled alongthe path of the missile passes between the electrodes and serves as the dielectric. The capacitor is connected in an arming circuit having a relay and a high potential source, the relay being in series with a detonating circuit. The electrodes are so calibrated that the space therebetween will not be conductive until the missile samples the highly ionized air in the trail of a jet aircraft. When this condition is reached the relay closes to energize the arming circuit which in turn energizes the detonating circuit. After the missile passes through the ionized air trail the capacitor is no longer conductive, deenergizing both circuits and detonating the missile.

A principal object of this invention is to provide a proximity fuse that will detonate a missile after is passes through and out of an ionized air trail of a jet target.

A further object is to provide a missile fuse which is positive in action, simple and low cost in construction, and having a high degree of reliability.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 shows diagrammatically the flight path taken by a missile having the fuse of the invention fired at a jet target creating an ionized air trail; and

FIG. 2 shows a partial section of the missile showing a schematic circuit diagram of the fuse.

Referring to FIG. 1, there is illustrated a typical flight path of a missile fired along a path 12 at a jet target Patented Sept. 5, 1961 14 in a tail-chase aspect. As is well known, the passage of the jet target through the atmosphere creates a cone 16 of ionized air which sampled by the fuse of this invention as presently described.

Missile 10 contains the usual components such as a primer, a detonaton'and a main explosive charge all of which may be represented by numeral 18 and which are controlled by the novel fuse of this invention schematically represented by the wiring diagram designated by reference numeral '20, The fuse comprises "two interconnected electrical circuits, which maybe considered as arr'ning and detonating circuits. The arming circuit containsan ion sensingmeans, such as a capacitor 22 havinga pair of spaced electrode plates so arranged that the air along missile path 12 passes therebetween and constitutes' a dielectric. In FIG. 2, the'no'se of the missile body is pro vided with an air pickup pas'sage'26, and the capacitor electnodes or plates are mounted on the inner wall'of passage 2 6 ai1'd insulated therefrom. In rain or turbo jet propelled missiles theplates can be positioned within the existing air'inlet, while in missiles incorporating percussion type fuses the air inlet may be laterally disposed on the missile nose. In otherinstances the insulated capacitor plates may be positioned on the skin of the missile in which construction the air about the missile is p ev A high potential source 28 is connected across the capacitor plates th'rbugha relay 30 having 'a switch 3-2. The capacitor plates are sci-calibrated that the enna! at mospheric'air'e'ncountered in the 'rriis'sile flight passing therebetween is sufliciently nonconductive to prevent a current flow between the plates, and the arming circuit is in a normally deenergized condition. When the missile samples the'highly ionized air in the targets trail the air breaks down as a dielectric and a current passes across the space between the plates. As this current is likely to be extremely small, relay '30 should be of a highly sensitive type. It may be found necessary to use a suitable conventional amplifying means in the circuit to ensure the availability'of a sufficiently high current. Relay switch 32 is connected in series with the detonating circuit which comprises a second potential source 34 and a second relay or solenoid 36 for detonating primer 18 at a predetermined time. For purposes of simplification relay 36 is shown as a solenoid type having a spring backed armature 38 the end of which is constructed as a firing pin for percussion firing of primer v18. It is obvious that the firing may be accomplished electrically by replacing the armae ture with a relay switch in a well known manner.

The operation of the fuse is as follows: As missile 10 travels along the flight path the normal atmospheric air passing'between the capacitor plates provides the dielectric, and the arming circuit, and in turn the detonating' circuits are deenergized. However, when the missile begins to sample the highly ionized air in the targets trail a point is reached where the dielectric breaks down permitting current to flow across the space between the' againsamples normal air having the dielectric charactertarget in a tail-chase aspect. The fuse is not armed until the missile enters the ionized air of a jet trail which constitutes a desirable safety feature, and the fuse will not detonate until the missile passes through and 'out of the jet trail and is alongside the target, which assures a high degree of lethality. Automatic calibration of the capacitor can be accomplished by connecting the electrodes to an altitude compensating means of a conventional type, and varying the air space or the distance between the electrodes as a function of altitude.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A missile for sensing a jet propelled target aircraft creating an exhaust trail of ionized air, comprising a body portion, an explosive charge in said body portion, a primer for igniting said charge and a fuse for igniting said primer, a fuse circuit including a current source in the missile and an ion sensing means, said means energizing, the circuit and arming the fuse when the missile enters the ionized trail, and said ion sensing means de-energizing the circuit to detonate the primer after the missile passes through the ionized trail.

2. A missile for sensing a jet propelled target aircraft creating an exhaust trail of ionized air, comprising a body portion, an explosive charge in said body portion, a primer for igniting said charge, and a fuse for igniting said primer, a fuse circuit including a current source in the missile and a capacitor for sampling the air in the targets path which forms the dielectric, said circuit being energized through said capacitor to armthe fuse when the missile enters the ionized trail, said circuit thereafter being de-energized through the capacitor to detonate the primer after the missile passes through the ionized trail.

3. The missile of claim 2 wherein said missile is provided with an inlet and said capacitor has a pair of elec trodes mounted in said passage in spaced relation to. permit the passage of air therebetween.

4. A missile for sensing a jet propelled aircraft creating a trail of ionized air, comprising a body portion, an explosive charge in said body portion, a primer for igniting said charge, a fuse for igniting said primer, said fuse comprising an arming circuit and a detonating circuit, said arming circuit including in series a capacitor in which the air in the path of the aircraft forms the dielectric, a first current source and a first relay, and said detonation circuit including in series a switch operable by said first relay, a second current source, and a relay capable of operating the primer, said circuits being energized when the missile enters the ionized air trail of the aircraft and de-energized when the missile passes through the ionized cone to detonate the primer.

References Cited in the file of this patent UNITED STATES PATENTS 1,311,781 Straub July 29, 1919 2,137,598 Vos Nov. 22, 1938 2,206,927 Turnbull July 9, 1940 2,505,042 Gourdon Apr. 25, 1950 2,536,327 Tolson Jan. 2, 1951 FOREIGN PATENTS 91,592 Sweden Feb. 24, 1938 

